1. Field of the Invention
The present invention generally relates to a drive circuit and a display unit, and more particularly, to a drive circuit and a display unit for controlling a display operation of a display device. Such a display device has a flat type panel and is used in portable equipment.
This application is a counterpart of Japanese patent application, Serial Number 127349/1998, filed May 11, 1998, the subject matter of which is incorporated herein by reference.
2. Description of the Related Art
Equipment having a display device, such as personal computers and word processors, are used in various fields. A flat panel type display device is often used in such equipment. This type of display device is also used in the portable telephone (or the mobile telephone). Flat panel type display devices include liquid crystal display devices, plasma display devices and devices using an electroluminescence phenomenon. The liquid crystal display device is the most commonly used. Recently, many types of equipment, such as the personal computer and the word processor, have become portable.
A drive circuit is used for driving a display panel part (for controlling the display operation) of the display device. For example, in the case of the liquid crystal display device, the drive circuit has a source driver arranged along one side (the long side of the rectangular display) of a TFT (Thin Film Transistor) display panel, and a gate driver arranged along the other side (the short side of the rectangular display panel) of the TFT display panel. The gate driver has a shift register which stores input data signals sequentially and outputs the stored data in parallel form, a level converting circuit (or a level shift circuit) which converts the signals from the shift register, and an output driver which adjusts the signals from the level converting circuit and outputs the thus adjusted signals. Such gate drivers are used for driving the display panel part. The conventional drive circuit, for example, is described in Japanese laid open patent No. 5-297817.
For example, the level converting circuit, which is one element of the gate driver, converts the respective levels of the output signals from the shift register. The level converting circuit converts voltage levels ranging from 0v (ground voltage) to 5v (power supply voltage) to voltage levels ranging from 0v to 30v. Hence, the level converting circuit consumes a lot of current according to the operation thereof. In fact, the level converting circuit is the element that consumes the most current in the gate driver. As mentioned above, using a plurality of gate drivers is necessary to drive the display panel part. A reduction in the current consumption of the gate driver is desired to thereby reduce the total current consumption of the display device as a whole. However, there have been no effective measures to satisfy this requirement in conventional techniques.
Even if the current consumption can be reduced, increasing the number of elements for driving the display device by adding a complex circuit to the display device must be avoided. Also to be avoided is increasing the cost by adopting complex development and process schemes. Furthermore, even if the current consumption can be reduced, the performance of the driving elements of the display device should not deteriorate.
In equipment having a battery-operated display device, there has been a strong demand to reduce current consumption.